Method of preparing mixed-salt lubricant compositions



United States Patent "Ctiice Patented Dec. 19, 1951 3,013,974 METHOD OF PREPARBNG MIXED-SALT LUBRECANT COMPQSHTIQNS Arnold Ii. Morway, Clark, and Albert J. Bodner, Linden,

NJ, assignors to Esso Research and Engineering Comparty, a corporation of Delaware No Drawing. Filed .l'uiy 31, 1959, tier. No. 830,736 6 Claims. (Cl. 252-69) This invention relates to lubricant compositions and methods for their preparation. Particularly, it relates to a method of preparing lubricating greases and fluids thickened with a mixed salt thickener including mixed calcium salts of acetic acid and straight chain fatty acids of 7 to 30 carbon atoms per molecule, whereby the thickener is formed at temperatures below 350 F.

There has recently been developed an important commercial class of greases thickened with dehydrated mixtures of calcium salts of a low molecular weight fatty acid in combination with calcium salts of C to C fatty acids wherein the mol ratio of low to higher molecular weight acids is about :1 to :1. Greases of this type have extremely good anti-wear characteristics, good loadcarrying ability, high dropping points, and many other desirable characteristics necessary for commercial success. One method of preparing this type of thickener is by a single step co-neutralization of all the acids in situ in the oil with an excess of lime, followed by heating to temperatures of about 430 F. and above. This high temperature results in obtaining the maximum thickening effect from the salt mixture. Similar preparation of the dehydrated grease, but at a lower temperature, e.g. 350 F., results in a much softer grease for the same amount of ingredients, which grease also had other different characteristics. However, the high temperature of manufacturing the thickener represents a decided disadvantage since temperatures of 400 F. and above can only be obtained by use of fire heated kettles or by use of nonvolatile heat-transfer fluids, such as Dowtherm or other similar circulating systems. A disadvantage with the fire heated kettles, of course, is the lire hazard. .The disadvantages of the heat-transfer fluid circulating systems are the expensive installation and the high cost of operation. Furthermore, many grease plants are not equipped with such high temperature equipment.

A second method had been found whereby greases having the maximum thickening power for a given amount of thickening material can be prepared at steam kettle temperatures of about 300 to 350 F. by carrying out the neutralization of the acids in several steps. Specifically, this second method involves: First, partially coneutralizing the mixed fatty acids in situ in an oil menstruum with about 90 to 99.5 wt. percent of the lime necessary for complete neutralization. Second, the partly neutralized reaction product is heated to temperatures of about 320 F., and maintained at this temperature until a thickening eifect is observed and the acidity has decreased to about 0.4% to 4.0% calculated as oleic acid. Third, a small amount of additional lime is added to completely neutralize all acidity and in fact to obtain about (M0 to 0.25% alkalinity calculated as NaOH. The grease is allowed to cool and may be finished by homogenizing, deaerating, etc. Thickeners prepared by this low temperature method are shown by X-ray diffraction to difier from the thickener prepared at high temperatures, but they do have the same maximum thickening effect. Unfortunately, however, they do not have the high loadcarrying ability of the thickener prepared at high temperatures. It has now been found and forms the subject of the present invention, that if the third step described above is carried out with calcium carbonate, instead of lime, extreme pressure properties are obtained. Thus, a

material fully comparable to the high temperature thick-.

ener results by adding sutficient calcium carbonate to obtain 0.5 to 1.0 wt. percent unreacted calcium carbonate in the finished grease.

The lubricating grease compositions encompassed by the method of this invention comprise a major amount of a lubricating oil and about 5 to 25, e.g. 8 to 20 wt. percent of the thickener. The thickener in turn comprises a mixture of the calcium salts of: acetic acid or its anhydride, and C to C fatty acids, and may also include C to C fatty acids. Usually about 1 to 20, e.g. 4 to 15 moles of acetic acid per mole of higher fatty acid will be used, while the higher fatty acid may be a mixture of 75 to 100 molar percent of the C to C fatty acid, with 0 to molar percent of C to C fatty acid.

The intermediate molecular weight fatty acids which can be used will include those straight chain, saturated acids such as capric, caprylic, nonanoic acid, lauric acid, etc. i

The high molecular weight carboxylic acids that can be used will include the saturated and unsaturated greasemaking fatty acids that are commonly known in the art.

In general, these fatty acids have from -14 to about'30 carbon atoms, preferably about 14 to 22 carbon atoms per molecule, and saponification values of from 300 to 150. Suitable fatty acids include myristic acid, palmitic acid, stearic acid, the various hydroxy stearic acids, oleic acid, arachidic acid, behenic acid and the like. Naturally occurring fatty acids such as fish oil acids, tallow acid,

etc. may also be utilized directly or after hydrogenation to decrease any undesirably high degree of unsaturation;

Mixtures of these high molecular weight fatty acids, e.g.

hydrogenated fish oil acids with oleic acid, in any propor tions, are also operable, as are fractions obtained by distillation, extraction or crystallization. Especially preferred are the hydroxy acids, e.g. IZ-hydroxy stearic.

If desired, various inorganic acids may be used to replace part of the low molecular weight fatty acid component in the preparation of the thickener. Thus, strong mineral acids such as hydrochloric acid, nitric acid, sulfuric acid, orthophosphoric acid and spent acids from sulfonation processes, may also be incorporated. Also, various inorganic salts may be used such as alkaline earth metal or alkali metal (e.g. sodium and lithium) nitrites, phosphates and chromates. An especially preferred inorganieacid is orthophosphoric acid, which is economical, and less corrosive to equipment than acetic acid. Furthermore, by using phosphoric acid to replace a portion of the acetic acid, the resulting grease is made more resistant to color and oxidation degradation than if no phosphoric acid was used. Also, phosphoric acid is not volatilized during the heating process as is acetic acid and therefore is easier to handle.

The lubricating oil used in the compositions of the invention may be either a mineral lubricating oil or:a'

synthetic lubricating oil.

For certain applications, it is preferred that the lubrieating oils used in preparing the grease be low viscosity solvent extracted parafiinic oils having a high viscosity index (V.I'.)'. These oils result in a transparent grease which is an advantage in many applications.- transparency permits the ready inspection of bearings 01 other parts which are being lubricated without the neces sity of first cleaning the parts.

prior calcium mixed salt greases which were prepared at high temperatures because they resulted in poorer structural stability, i.e. the grease'tended to fluidize upon shearmg. However, when the thickener is prepared at the lower temperatures of the method of the present inven-' Thus, such Previously, such high V.I. parafiinic oils. were not used commercially in the finic oils for this purpose should have a V.I. of about 85 to 110, preferably 95 to 105, and a viscosity at 210 F. of 35 to 90, preferably 40 to 55. Such oils are obtainable from paraffinic base crude petroleum. Alternately, mixed base or Mid-continent distillates are extracted with phenol, the low V.I. fractions are dissolved in the phenol and the high V.I. raflinate is furtherpurified by distillation and filtration by processes well known in the refining art.

Various other additives may also be added to the lubricating composition (e.g. 0.1 to 10.0 weight percent based on the total weight of the composition), for example, oxidation inhibitors such as phenyl-alpha-naphthylamine; corrosion inhibitors, such as sorbitan monooleate; supplemental grease thickeners such as polyethylene and polypropylene; stabilizers such as aluminum hydroxy stearate, and the like.

In general, the compositions of the invention will be prepared as follows, wherein all pants are by weight. About 8 to 16 parts of acetic acid or an equivalent amount of its anhydride (optionally with about 1 to 3 parts by weight of an inorganic mineral acid or a mineral acid salt), and about 4 to 8 parts of a C to C fatty acid and to 35 parts by weight of C to C fatty acid and lime are dispersed in the lubricating oil. The amount of lime used should be within the range of 4 to 12 parts, sufficient to obtain about 2.0 to 10.0% acidity (expressed as oleic acid) as measured by ASTM D-664 method of determination for free acidity or alkalinity. Next, the partially neutralized mixed acid-oil blend is heated to a temperature of about 300 to 350 F., preferably 320 to 340 F. for about 1 to 8, e.g. 2 to 4 hours or until the acidity is decreased to about 0.4 to 4.0%. At this point 0.1 to 2.0 parts by weight of CaCO is added so as to achieve a final alkalinity of about 0.5 to 1.0% when measured as equivalent NaOH (Method ASTM D664). The mixture may then be cooled to about 200 to 210 R, where conventional additives, if any, may be added. The grease is then cooled to below 110 P. where anticorrosion additives such as NaNO may be added. The grease may then be homogenized as by passing through a Gaulin homogenizer or a Charlotte mill, followed by subsequent cooling to room temperature.

The invention will be further understood by the following examples:

Example I-A (all parts by weight).-Grease prepared by the method of the invention 71.4 parts of mineral lubricating oil having a viscosity of 55 SUS at 210 F. and a V.I. of about 60, 8.2 parts of hydrated lime and 2 parts of commercial 12-hydroxy stearic acid were intimately mixed in a steam heated kettle. A blend of 12 parts of glacial acetic acid and 4 parts of Wecoline AAC acids (coconut fatty acid consisting of 28 wt. percent caprylic, 46 wt. percent capric and 26 wt. percent lauric acids) were next added to the kettle and mixed into the composition without external heating. The amount of lime used was insuflicient to completely neutralize the acids present and the composition showed a free acidity equivalent to 2.35 wt. percent oleic acid. Heating was then initiated and the temperature of the composition raised to 320 F. and maintained for about 2 hours until a firm homogeneous dehydrated grease structure formed. A free acid determination at this point showed that the free acidity had decreased to 0.49 wt. percent oleic acid. Next, 1.4 wt. percent of a finely ground dry calcium carbonate was added to the composition and a free alkalinity equivalent to 0.95 wt. percent NaOH resulted. Stirring was continued for another half .hour following which the grease was rapidly cooled by passing cold water through the kettle jacket while stirring. When the temperature had dropped to 200 F., one part of phenyl a-naphthylamine as an oxidation inhibitor was added. The grease was then further cooled to 100 F., where 2 parts of finely ground NaNO were added. Next, the grease was homogenized in a Gaulin homogenizer at 5,000 p.s.i.

Example I-B.-C0mplete neutralization with lime I-A I-B High Alknlinity- Low Alkalinity- Excess CaCO; Excess Lime F or m 111 a t to 11 Weight):

Glacial Acetic Acid Wecoline AAC Acids lz llydroxy Stearlc Acid Hydrated Lime Phenyl a-Naphthylamine Calcium Carbonate Mineral Lubricating Oil of 55 SUS. at 210 F.

Properties:

Appearance Excellent, smooth (Percent Excellent, smooth grease. Dropping Point, F 500+ 500+. Penetration, 77 F., mm./

Unworked Worked 60 Strokes.-- Worked 100,000

Strokes. 4 Hour Shell Roller Test- Penetration Micro mrn./10:

Before After Wheel Bearing Test1 Hr.

Tilted 220 1?., Leakage, Percent.

Almen Test Wgt-s.-

Gradual Loading 1;) Pin Condition Shock Loading (Max). Pin Condition Timken Test 45 lbs. Load.

Solubility in Boiling Water.

Carries l0 Wgts.

12 Wgts.

Borderline Puss Wide Scar. Insoluble.

As seen by the preceding table, Example I-A of the invention was superior to the grease of the prior method (IB) with regard to load-carrying ability as illustrated by the Almen and Timken tests. Thus, the grease of Example I-B could only carry 10 weights in a gradual loading Almen test and only 12 weights under shock loading, while the grease of Example I-A carried 15 weights in both tests. The load-carrying ability of the grease of I-B can be increased by increasing the amount of excess lime present in the grease, however, this will result in poor structural stability. To illustrate, if Example I-B is repeated using sufiicient lime to obtain an excess of lime equivalent to about .9 wt. percent NaOH, the resulting grease would show an ASTM penetration of about 375 to 390 mm./l0 when worked 10,000 strokes. On the other hand, by using the calcium carbonate, the grease of Example I-A had an ASTM penetration of 341 mm./ 10 when worked 100,000 strokes. It is believed that the adverse efiect of excess lime upon structural stability of the grease is due to the polarity of the lime, while calcium carbonate on the other hand is inert in this respect.

To further illustrate the invention, Example I-A may be repeated using a solvent extracted paraffinic mineral oil having a viscosity index (Dean & Davis) of and a viscosity at 210 F. of 50 SSU in place of the mineral lubricating oil used in Example 'I-A. As previously mentioned, the use of a high V.I., low viscosity solvent extracted paraifinic mineral oil improves the transparency of the lubricating grease and better adapts it for certain applications.

What is claimed is:

1. A method of preparing a dehydrated lubricant comprising a major proportion of a lubricating oil and about 5 to 25 wt. percent of a mixed salt thickener, said thickener comprising as the principal ingredients, calcium salts of about 1 to 20 molar proportions of acetic acid and one molar proportion of a C to C fatty acid, said method comprising partially neutralizing a dispersion of said acids in at least a part of said lubricating oil with an amount of lime such that the partially neutralized mixture has an acidity of about 2 to 10% in terms of oleic acid, heating said partially neutralized mixture at a temperature of about 300 to 350 F. until said acidity is reduced to about 0.4 to 4.0% in terms of oleic acid, then neutralizing the remaining acidity with sufficient CaCO to obtain an alkalinity of 0.5 to 1.0 wt. percent in terms of NaOH, followed by cooling to form said grease.

2. A method according to claim 1, wherein said C to C fatty acid is a mixture of a C to C acid and a C14 to C30 acid.

3. A method according to claim 1, wherein said lubricating oil is a mineral oil.

4. A method according to claim 2, wherein said C to C acid is 12-hydroxy stearic acid.

5. A method according to claim 3, wherein said mineral oil has a viscosity index of 85 to 110, a viscosity at 210 F. of 35 to 90 SUS. and is a solvent extracted parafiinic oil.

6. A method of preparing a dehydrated lubricant comprising a major proportion of mineral lubricating oil and 5 to 25 wt. percent of a mixed salt thickener, said thickener consisting essentially of calcium salts of about 4 to 15 molar proportions of acetic acid per molar proportion of a C to C fatty acid, wherein said lubricant is prepared by partially neutralizing a dispersion of said acids in said lubricating oil with an amount of lime such that the partially neutralized mixture has an acidity of about 2 to 10% in terms of oleic acid, heating said partially neutralized mixture at a temperature of 320 to 340 F. for about 1 to 8 hours until the acidity has decreased to about 0.4 to 4.0 Wt. percent in terms of oleic acid, neutralizing the remaining acidity with suilicient CaCO to obtain an alkalinity of .5 to 1.0 wt. percent as equivalent to NaOH, and cooling to form said grease.

References Cited in the tile of this patent UNITED STATES PATENTS 2,846,392 M'orway et al. Aug. 5, 1958 2,850,457 Thompson et al Sept. 2, 1958 2,850,458 Beerbower et al Sept. 2, 1958 2,898,297 Schott Aug. 4, 1959 

1. A METHOD OF PREPARING A DEHYDRATED LUBRICANT COMPRISING A MAJOR PROPORTION OF A LUBRICATING OIL AND ABOUT 5 TO 25 WT. PERCENT OF A MIXED SALT THICKENER, SAID THICKENER COMPRISING AS THE PRINCIPAL INGREDIENTS, CALCIUM SALTS OF ABOUT 1 TO 20 MOLAR PROPORTIONS OF ACETIC ACID AND ONE MOLAR PROPORTION OF A C7 TO C30 FATTY ACID, SAID METHOD COMPRISING PARTIALLY NEUTRALIZING A DISPERSION OF SAID ACIDS IN AT LEAST A PART OF SAID LUBRICATING OIL WITH AN AMOUNT OF LIME SUCH THAT THE PARTIALLY NEUTRALIZED MIXTURE HAS AN ACIDITY OF ABOUT 2 TO 10% IN TERMS OF OLEIC ACID, HEATING SAID PARTIALLY NEUTRALIZED MIXTURE AT A TEMPERATURE OF ABOUT 300* TO 350*F. UNTIL SAID ACIDITY IS REDUCED TO ABOUT 0.4 TO 4.0% IN TERMS OF OLEIC ACID, THEN NEUTRALIZING THE REMAINING ACIDITY WITH SUFFICIENT CACO2 TO OBTAIN AN ALKALINITY OF 0.5 TO 1.0 WT. PERCENT IN TERMS OF NAOH, FOLLOWED BY COOLING TO FORM SAID GREASE. 